Tire Ruler255/55R18 dimensions
| Overall diameter (height) | 29.04″ · 738 mm |
| Section width | 10.04″ · 255 mm |
| Sidewall height | 5.52″ · 140 mm |
| Wheel diameter | 18″ |
| Rim width (rule of thumb) | 7–9″ |
| Circumference | 91.2″ |
| Revolutions per mile | 694 |
| In inches (flotation style) | 29.0 × 10.0R18 |
How it’s calculated: the sidewall is 55% of the 255 mm width = 140.3 mm (5.52″). Add two sidewalls to the 18″ wheel: 18 + 2 × 5.52 = 29.04″.
Bigger tires than 255/55R18 on 18″ wheels
| Size | Height | Taller by | 60 mph reads |
|---|---|---|---|
| 245/60R18 | 29.6″ | +0.53″ (+1.8%) | 61.1 mph |
| 235/65R18 | 30.0″ | +0.98″ (+3.4%) | 62.0 mph |
| 265/60R18 | 30.5″ | +1.48″ (+5.1%) | 63.1 mph |
| 245/65R18 | 30.5″ | +1.50″ (+5.2%) | 63.1 mph |
| 275/60R18 | 31.0″ | +1.95″ (+6.7%) | 64.0 mph |
“60 mph reads” is your real speed when a speedometer set up for 255/55R18 shows 60. Above about 3% taller, most trucks need a leveling kit or lift, and the speedometer should be recalibrated.
Sizes equivalent to 255/55R18
Within 1.5% of the same height on an 18″ wheel. Usually interchangeable for the speedometer; check width, load index and clearance.
| Size | Height | Width | Difference |
|---|---|---|---|
| 235/60R18 | 29.1″ | 9.3″ | +0.2% |
| 225/60R18 | 28.6″ | 8.9″ | −1.4% |
Same height on a different wheel size
Changing wheel size (plus or minus sizing) while keeping the overall height keeps your speedometer right:
- 235/75R15: 28.9″ tall on a 15″ wheel (−0.6%)
- 225/75R16: 29.3″ tall on a 16″ wheel (+0.8%)
- 235/70R16: 29.0″ tall on a 16″ wheel (−0.3%)
- 235/65R17: 29.0″ tall on a 17″ wheel (−0.1%)
- 235/55R19: 29.2″ tall on a 19″ wheel (+0.5%)
- 255/50R19: 29.0″ tall on a 19″ wheel (−0.0%)
- 255/45R20: 29.0″ tall on a 20″ wheel (−0.0%)
- 245/45R20: 28.7″ tall on a 20″ wheel (−1.2%)
- 265/45R20: 29.4″ tall on a 20″ wheel (+1.2%)
- 275/40R20: 28.7″ tall on a 20″ wheel (−1.3%)
Frequently asked questions
Is 255/55R18 a 29 inch tire?
Yes. 255/55R18 is 29.04 inches tall, so it's sold and talked about as a 29-inch tire.
What size is 255/55R18 in inches?
255/55R18 is 29.0 inches tall (overall diameter), 10.0 inches wide, with a 5.5 inch sidewall, and fits an 18 inch wheel.
What tire size is equivalent to 255/55R18?
Sizes within 1.5% of the same diameter on an 18" wheel: 235/60R18 (29.1"), 225/60R18 (28.6"). Check load index and width before swapping.
What rim width fits 255/55R18?
As a rule of thumb, about 7–9 inches. The tire maker's spec sheet lists the approved range for each model.
How many revolutions per mile does 255/55R18 make?
About 694 revolutions per mile in theory (circumference 91.2 in). Real tires turn slightly more because they flatten under load.